1. Field of the Invention
This invention is directed to a process for the purification of coal-derived liquids, specifically, a process by which coal liquids may be fractionated to isolate a low Conradson Carbon Residue (CCR) maltenic fraction, a high CCR asphaltenic fraction and at the same time remove solid impurities. This invention is further directed to the use of a distillation separatory process to establish a concentration gradient between a high polarity and a low polarity solvent within an extraction column, and the integration of this distillation process with additional processes to provide economic and efficient production of liquefied coal fuel sources.
2. Description of the Prior Art
As petroleum resources become increasingly scarce and expensive, an important step in making coal liquefaction processes more commercially attractive will stem from improvements in solid/liquid separation, an essential step prior to the coal-liquid's use as a fuel. Unlike petroleum residua, liquefied coal contains significant quantities of solid material from various sources: (a) ash and mineral matter from the original coal, (b) attrited and/or entrained catalyst from the liquefaction step, and (c) unconverted coal. The mineral matter in particular is highly dependent upon the coal source employed and is variable with any given coal seam.
In some coal liquefaction designs some of the solid is moved by a bank of hydroclones. In other processes the solid is eliminated by filtration; some configurations employ a deasphalting step. Many of these single step deashing operations produce a single reject stream including both solids and low quality asphaltic bottoms. Other multi-step schemes utilize filtration or solvent dilution, followed by settling. By employing a system comprising a distillation-induced polarity gradient extraction of the liquefied coal, the inventors have discovered a new process which achieves both solids recovery and liquid product fractionation in a single operation.